1. Field of the Invention
The present invention relates generally to a Multimedia Broadcast/Multicast Service (MBMS), and in particular, to a method for managing an MBMS service context for an MBMS.
2. Description of the Related Art
Recently, due to the development of communication technology, a service provided in a Wideband Code Division Multiple Access (WCDMA) mobile communication system is developing into multimedia broadcast/communication capable of supporting an existing voice service and also packet service and multimedia service that transmit mass data, such as packet data and circuit data. In order to support the multimedia broadcast/communication, an MBMS service has been proposed, in which a particular service is provided from one or several data sources to a plurality of user equipments (UEs).
The “MBMS service” refers to a service for transmitting the same multimedia data to a plurality of recipients through a radio network. In the MBMS service, recipients can share one radio channel to save radio transmission resources. The MBMS service supports transmission of multimedia data such as real-time image and voice, still image, and text, and can simultaneously transmit voice data and image data according to a type of the multimedia transmission. As such, the MBMS service requires massive transmission resources. Further, because the same data must be transmitted to a plurality of cells where users are located, connections are made on a point-to-point (PtP) basis or a point-to-multipoint (PtM) basis, based on the number of users located on each cell.
FIG. 1 is a diagram schematically illustrating nodes joining an MBMS service in a mobile communication network. Referring to FIG. 1, UEs 161, 162, 163, 171, and 172 are terminal equipments or subscribers for receiving an MBMS service, and a cell #1 160 and a cell #2 170 are controlled by their own base station apparatuses or Node Bs, which wirelessly transmit MBMS-related data to subscribers. A radio network controller (RNC) 140 controls the cells 160 and 170, selectively transmits multimedia data to a particular cell, and controls a radio channel set up to provide an MBMS service. Connection between the RNC 140 and the UEs 161 and 172 are called “radio resource control (RRC) interfaces.”
The RNC 140 is connected to a packet switched or packet service (PS) network such as the Internet by a serving GPRS (General Packet Radio Service) support node (SGSN) 130. Communication between the RNC 140 and the PS network is achieved by packet switched (PS) signaling. Particularly, a connection between the RNC 140 and the SGSN 130 is called an “Iu-PS interface.”
The SGSN 130 controls an MBMS service for each subscriber. For example, typical functions of the SGSN 130 include managing service accounting-related information of each subscriber and selectively transmitting multimedia data to the particular RNC 140.
A transit network (NW) 120 provides a communication path between a broadcast multicast service center (BM-SC) 110 and the SGSN 130, and can be connected to an external network via an undepicted gateway GPRS support node (GGSN). The BM-SC 110 is a source of MBMS data, and controls scheduling of MBMS data.
The RNC 140 is connected to a circuit switched (CS) network by a mobile switching center (MSC) 150. The “CS network” is a connection-based voice-oriented legacy communication network. Communication between the RNC 140 and the MSC 150, and is achieved by circuit switched (CS) signaling. Particularly, a connection between the RNC 140 and the MSC 150 is called an “Iu-CS interface.” An MBMS data stream is transferred to the UEs 161, 162, 163, 171, and 172 via the transit network 120, the SGSN 130, the RNC 140, and the Node Bs 160 and 170.
Although not illustrated in FIG. 1, for one MBMS service, a plurality of SGSNs and a plurality of RNCs for each SGSN can be used. Each of the SGSNs selectively transmits data to its RNCs, and each of the RNCs selectively transmits data to its cells. A list of nodes to which a data stream should be transmitted is stored in the SGSN and RNC (i.e., a list of RNCs is stored in each SGSN, and a list of cells is stored in each RNC), to later selectively transmit MBMS data only to the nodes stored in the list.
In order for UEs to access a network and receive a service therefrom, a context, which is a set of information necessary for providing the corresponding service, must be first created between the UEs and network nodes. A UE context and an MM (Mobility Management) context are conventional examples of a context.
An RNC creates a UE context for UEs after setting up RRC connection. The UE context includes fundamental information such as a UE identity (ID), position information of a UE, RRC state information of the UE, and information on a radio resource assigned to the UE. Further, the UE context is managed by an RNC while RRC connection is activated.
The MM context is used to manage a position of a UE in a core network (CN). In order for a UE to receive a PS service, an MM context of the UE must be first created in an SGSN and a GGSN through a GPRS Attach procedure. Particularly, an MM context of the SGSN includes UE ID such as IMSI (International Mobile Subscriber Identity), P-TMSI (Temporary Mobile Subscriber Identity), IMEI (International Mobile Equipment Identity), and MS-ISDN (Mobile Subscriber ISDN (Integrated Switched Data Network)) Number, position information such as RA (Routing Area) and SAC (Service Area Code), authentication/encryption-related information, accounting information, and DRX (Discontinuous Reception) parameters.
Network nodes, such as an RNC, an MSC, and an SGSN manage a state of a UE for efficient signaling transmission and data transmission. In particular, the RNC manages an RRC state of a UE, and the RRC state is determined according to an RRC connection of the UE being set up. A state in which the RRC connection is set up is called an “RRC-Connected state,” and a state in which RRC connection is not set up is called an “RRC-Idle state.”
The SGSN manages a PMM (Packet Mobility Management) state of a UE. A UE for which an MM context is not created in an SGSN is identified as a UE in a PMM-Detached state. A UE for which an MM context is created in an SGSN through a GPRS Attach procedure is divided into a UE in a PMM-Connected state and a UE in a PMM-Idle state. A state in which a UE has Iu-PS signaling connection and is in an RRC-Connected state is called a “PMM-Connected state.” A state in which a UE does not have Iu-PS signaling connection or is in an RRC-Idle state is called a “PMM-Idle state.” The MSC manages a CMM (Circuit Mobile Management) state of a UE. A state in which a UE has Iu-CS signaling connection and is in an RRC-Connected state is called a “CMM-Connected state, and a state in which a UE does not have Iu-CS signaling connection or is in an RRC-Idle state is called a “CMM-Idle state.”
For UEs requesting an MBMS service, an MBMS service context and an MBMS UE context are used in network nodes for the MBMS service. Because the MBMS service simultaneously transmits the same information to a plurality of UEs, an MBMS service context is uniquely created for each MBMS service or each session in an MBMS service, rather than being individually created for each UE. The MBMS UE context stores information on an MBMS service that each UE joined.
In order to perform an MBMS service, an MBMS service context must first be created in UEs and a BM-SC, which are front-end points of the MBMS service. Also, an MBMS service context is created in an RNC, SGSN, and GGSN, which are network nodes used for transmitting MBMS data.
In a PS network represented by an RNC and an SGSN, because information related to a UE in a PMM-Idle mode is not included in an MBMS service context of an RNC, the UE may fail to receive an MBMS paging from the PS network. This phenomenon can occur when although RRC connection for a circuit switched (CS) service is set up between a UE and an RRC, the PS network does not recognize this fact.
FIG. 2 is a diagram illustrating an operation occurring when a UE is in a PMM-Idle mode while managing RRC connection set up to an RNC (RRC-Connected state) in a conventional MBMS system. In FIG. 2, reference numeral 202 represents a UE receiving an MBMS service, reference numeral 204 represents a serving RNC (SRNC) for an MBMS service, which is associated with the UE 202, and reference numeral 206 represents an SGSN of a CN for the MBMS service.
The UE 202 is in a PMM-Idle mode where it joined an MBMS service but does not have a PS signaling. Referring to FIG. 2, in step 210, the UE 202 sets up an RRC connection for receiving a CS service, and transitions to a Cell-FACH (Forward Access Channel) or Cell-DCH (Dedicated Channel) state of an RRC-Connected mode. In step 220, the SGSN 206 detects start of an MBMS service through an MBMS Session Start message received via a BM-SC. The MBMS Session Start message includes MBMS service ID, multicast area information, and QoS (Quality of Service) information.
In step 230, the SGSN 206 searches for an MBMS service context corresponding to the MBMS service identified by an MBMS service ID included in the MBMS Session Start message, and transfers the MBMS. Session Start message to RNCs belonging to an RNC list included in the MBMS service context, and all RNCs belonging to RA (Routing Area) to which UEs in a PMM-Idle state belong, in order to inform the RNCs that transmission of MBMS data is started.
In step 240, the RNC 204 analyzes an MBMS service ID in the MBMS Session Start message received from the SGSN 206 in order to page UEs that are requesting the MBMS service. Here, because the MBMS Session Start message transmitted in step 230 does not include a UE ID, the SRNC 204 detects IDs of UEs joined the MBMS service using the MBMS service ID included in the MBMS Session Start message.
In an MBMS paging procedure, the SRNC 204 calculates the same PO (Paging Occasion) and PI (Paging Instance) values using the MBMS service ID (for example, TMGI) and a DRX parameter. The SRNC 204 turns on or off a pilot indication channel (PICH) for a time period indicated by the PI and the PO to indicate whether a related paging channel (PCH) for UEs is received, and pages the UEs through a related PCH that starts a predetermined time after the PICH. Here, in order to page UEs in a Cell-DCH state, a Paging Type 2 message transmitted over a dedicated control channel (DCCH) is used.
However, if the SRNC 204 deletes information on a relation between a certain UE 202 and the MBMS service as illustrated in step 240, while the UE 202 switches to a PMM-Idle mode, the SRNC 204 cannot transmit the Paging Type 2 message to the UE 202 as illustrated in step 250.
That is, the SRNC 204 uses a common channel (CCH) to page UEs in a PMM-Idle mode. However, because the UE 202 actually has a dedicated channel for a CS service with a CS network, it cannot receive an MBMS paging over the common channel. Undesirably, therefore, the UE 202 cannot receive MBMS data although it has requested an MBMS service.